Endodontic system and method

ABSTRACT

The present invention provides a system for the endodontic treatment of a root canal, comprising
         (i) an endodontic instrument;   (ii) an endodontic handpiece having a drive motor for rotating the endodontic instrument releasably attached to the handpiece;   (iii) a control unit for controlling the rotation of the endodontic instrument according to one or more predetermined rotational sequences;
 
the rotational sequences comprising reciprocating the endodontic instrument by continuously sequentially rotating the endodontic instrument in a first direction followed by reversing the direction of rotation so that
       

       0.5×Ψ≦α&lt;Ψ and 3≦α/β≦20,
 
     wherein α represents a rotational angle in a direction in which the rotating endodontic instrument removes debris from the root canal, β represents a rotational angle in the opposite direction, and Ψ represents the elastic angle of the endodontic instrument at which plastic deformation occurs in the direction of α.

RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.13/267,272 filed Oct. 6, 2011 and European patent application number EP10013364.4 filed Oct. 6, 2010.

FIELD OF THE INVENTION

The present invention relates to a system for the endodontic treatmentof a root canal. Furthermore, the present invention also relates to amethod for operating the system for the endodontic treatment of a rootcanal.

BACKGROUND OF THE INVENTION

Effective cleaning and shaping of the root canal system is essential forachieving the biological and mechanical objectives of root canaltreatment (Sjögren et al. 1997). The objectives are to remove all thepulp tissue, bacteria and their by-products while providing adequatecanal shape to fill the canal.

Traditionally, the shaping of root canals was achieved by the use ofstainless steel hand files. However, techniques using stainless steelhand files have several drawbacks:

-   1. They require the use of numerous hand files and drills to    adequately prepare the canals (Schilder 1974).-   2. Hand instrumentation with stainless steel files is time consuming    (Ferrazetal. 2001).-   3. The stainless steel hand instrumentation techniques have an    increased incidence of canal transportation (Kuhn et al. 1997, Reddy    & Hicks 1998, Ferraz et al. 2001, Pettiette et al. 2001).-   4. Finally, from a clinical standpoint, the use of hand instruments    in narrow canals can be very frustrating especially in teeth with    difficult access.

Moreover, canal curvature has always introduced complexity into canalpreparation. The “balanced force concept,” i.e. small clockwise andcounter clockwise movements, was developed over a period of 12 years,and proposed in 1985 by Roane as a means of overcoming the curvatureinfluence. Using the balanced force technique, it is possible to shapecurved canals with larger diameter hand instruments. The use ofstainless steel hand instruments, however, is time-consuming andstrenuous, and there is a high frequency of preparation errors.

The development of continuous rotary preparation with nickel-titaniuminstruments solved some of these issues, although it is still necessaryto use several hand and rotary files in different steps, and there maybe a lengthy learning curve before proficiency can be achieved. In fact,NiTi instruments offer many advantages over conventional stainless steelfiles. They are flexible (Walia et al. 1988), have increased cuttingefficiency (Kazemi et al. 1996) and have improved time efficiency(Ferraz et al. 2001). Furthermore, NiTi instruments maintain theoriginal canal shape during preparation and have a reduced tendency totransport the apical foramen (Kuhn et al. 1997, Reddy & Hicks 1998,Ferraz et al. 2001, Pettiette et al. 2001).

However, as these techniques also require the use of numerousinstruments to enlarge the canal to an adequate size and taper, they arerelatively time consuming.

Also, the use of hand instruments (for example to create a glide pathprior to using a rotary instrument), which can be very frustrating innarrow canals in teeth with a limited access, is required. Withcontinuous rotary NiTi systems it is necessary to create a glide path inorder to minimize the risk of fracture. During the use of a rotaryinstrument, the tip of the instrument may bind in the canal. The motorwill keep rotating the instrument while the tip of the instrument isbound. The instrument will rotate past its plastic limit and willeventually fracture at a specific angle of rotation. For this reason, itis necessary to create an initial glide path, or a minimal canalenlargement, before using continuous rotary instruments. The glide pathwill minimize the incidence of instrument binding and, therefore,minimize the risk of fracture.

The use of only one engine-driven instrument in reciprocation to preparea root canal was published in the International Endodontic Journal(Yared 2008). The article described the use of an F2 ProTaperinstrument. However, the use of that instrument in reciprocationpresented two drawbacks:

1. Instrument fracture by cyclic fatigue in relation to the relativerigidity of the instrument due to its size, taper and cross-section.2. The necessity of creating a glide path with additional hand filesprior to using the F2 instrument in reciprocation.

SUMMARY OF THE INVENTION

It is the problem of the present invention to provide a system for theendodontic treatment of a root canal wherein only a single instrument isrequired to enlarge the canal and wherein hand files for enlarging theroot canal prior to using the single file are not required, and wherebyeven a narrow and curved canal, may be prepared to an adequate size andtaper.

Moreover, it is the problem of the present invention to provide a methodfor operating an endodontic system for the endodontic treatment of aroot canal wherein only a single instrument is required to enlarge thecanal and wherein hand files for enlarging the root canal prior to usingthe single file are not required, and whereby even a narrow and curvedcanal may be prepared to an adequate size and taper.

Accordingly, the present invention provides a system for the endodontictreatment of a root canal, comprising an endodontic instrument; anendodontic handpiece having a drive motor for rotating the endodonticinstrument releasably attached to the handpiece; a control unit forcontrolling the rotation of the endodontic instrument according to oneor more predetermined rotational sequences; the rotational sequencescomprising reciprocating the endodontic instrument by continuouslysequentially rotating the endodontic instrument in a first directionfollowed by reversing the direction of rotation so that

0.5×Ψ≦α≦Ψ and 3≦α/β≦20,

wherein α represents a rotational angle in a direction in which therotating endodontic instrument removes debris from the root canal, βrepresents a rotational angle in the opposite direction, and Ψrepresents the elastic angle of the endodontic instrument at whichplastic deformation occurs in the direction of α.

Moreover, the present invention relates to a method for operating thesystem for the endodontic treatment of a root canal, the methodcomprising reciprocating an endodontic instrument by continuouslysequentially rotating the endodontic instrument in a first directionfollowed by reversing the direction of rotation so that

0.5×Ψ≦α≦Ψ and 3≦α/β≦20,

wherein α, β, and Ψ are as defined above. x in the formulae indicatesthe mathematical operation of multiplication and / indicates themathematical operation of division.

The present invention is based on the recognition that root canalpreparation may be accomplished using only a single specificengine-driven instrument in reciprocation and without prior hand filing.This new concept goes against the current teaching standard, whichrequires the gradual enlargement of the canal with differentfiles/instruments until the desired shape is obtained. In particular,the system and method of the present invention does not require thecreation of a glide path with smaller instruments prior to using ashaping instrument to minimize the incidence of fracture. According tothe present invention, the shaping instrument will follow the existingand natural path of least resistance, which is the root canal, which isnot only time-saving but also particularly convenient in teeth withlimited access. Additionally, errors associated with the use of handfiling prior to using mechanically driven instruments can be avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a system for the endodontictreatment of a root canal according to the present invention.

FIG. 2 shows an endodontic instrument used in the system of the presentinvention.

FIG. 3 shows an example of a diagram for determining the elastic angle Ψof an endodontic instrument used according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a system for the endodontic treatment of a root canal inaccordance with one embodiment of the present invention. The system 2comprises a handpiece 10 and a control unit 20.

An endodontic file 11 is releasably secured in a chuck of the handpiecehead 12. The handpiece 10 further comprises a drive motor 14 fastened toa contra angle 13. The drive motor 14 is connected by a cable 5 to thecontrol unit 20 which includes a microprocessor 9. The control unit 2may further contain a memory 1, a keyboard 6 and a display 7. Thecontrol unit 20 controls the drive motor 4. Thereby, the control unit 20controls the rotation of the endodontic instrument 11 according to oneor more predetermined rotational sequences. In a cordless embodiment,the control unit 20 may be incorporated into the handpiece 10 and thesystem is battery operated. In a preferred embodiment, the drive motoris battery operated.

A memory 1 may be used to store predetermined rotational sequences foran endodontic treatment; as well as a library of operational parameters.

In accordance with the invention, the microprocessor 9 is configured toexecute a predetermined rotational sequence. The predeterminedrotational sequence comprises reciprocating the endodontic instrument bycontinuously sequentially rotating the endodontic instrument in a firstdirection followed by reversing the direction of rotation so that

0.5×Ψ≦α≦Ψ and 3≦α/β20,

wherein α represents a rotational angle in a direction in which therotating endodontic instrument removes debris from the root canal, βrepresents a rotational angle in the opposite direction, and Ψrepresents the elastic angle of the endodontic instrument at whichplastic deformation occurs in the direction of α. In reciprocation, theendodontic instrument is driven first in a cutting direction and thenreverses to release the instrument. According to the present invention,the angles of reciprocation are precise and specific to the design ofthe endodontic instrument and to the drive motor. One complete rotationof 360° is completed in several reciprocating movements.

According to an alternative embodiment, the control unit may beimplemented as a mechanical means which does not require electric energyfor controlling the rotational sequence.

According to a preferred embodiment, the reciprocating of the endodonticinstrument is controlled so that 0.7×Ψ≦α<0.9×Ψ, and Ψ and α are asdefined above. According to a further preferred embodiment, thereciprocating of the endodontic instrument is controlled so that3.5≦α/β≦20, more preferably 4.0≦α/β≦10 and α and β are as defined above.The elastic angle Ψ of the endodontic instrument at which plasticdeformation occurs in the direction of α is determined based on DIN ENISO 3630-1:2008-04. Specifically, the test is carried out on aninstrument to determine the elastic torque limit and the elastic angle,whereby the endodontic instrument is fixed at 3 mm from the tip androtated at 2 rpm until fracture occurred. The function of the elastictorque over the rotational angle in the direction of α is recorded. Theelastic angle value Ψ is calculated by the interpretation of the graphobtained during the torque resistance test as illustrated in FIG. 3.Specifically, the elastic angle is the intersection of the tangent ofthe region of elastic deformation and the tangent tangent of the regionof plastic deformation of the endodontic instrument as represented in atorque diagram as shown in FIG. 3. The elastic angle value Ψ may beconsidered as the limiting rotational angle where any further rotationwill result in a permanent plastic deformation of the endodonticinstrument. The elastic angle value Ψ depends on the material and theshape of the endodontic instrument.

According to a further preferred embodiment the endodontic instrumenthas an elastic angle Ψ in the range of from 120 to 420°, more preferably150 to 400° and still more preferably 190 to 390°. The preferredmaterial for the endodontic instrument used according to the inventioncomprises a NiTi alloy.

According to a further preferred embodiment, the control unit furthercontrols one or more parameters of the rotational sequence, saidparameters being selected from the frequency of reciprocation (F_(r)),the number of reciprocation cycles (N_(r)) and the torque (T_(r))exerted on the file.

According to the invention, the specific value of determines the limitsof α and β. Accordingly, if, for example, Ψ is 240° for a givenendodontic instrument, then α as the rotational angle in a direction inwhich the rotating endodontic instrument removes debris from the rootcanal is in the range of from 120° to less than 240°. Selecting α to be180°, then β as the rotational angle in the opposite direction is in therange of from 9° to 60°. According to the invention, it is preferred toincrease the difference between α and β in the rotational sequence sothat the efficiency of the system is improved.

Furthermore, according to a preferred embodiment, the control unit ofthe system of the present invention may also use Ψ to determine F_(r),N_(r), and/or T_(r).

Furthermore, the control unit may control the frequency of reciprocation(Fr) in a range of from 5 to 30 Hz, more preferably in a range of from 5to 20 Hz.

FIG. 2 a shows an embodiment of a preferred endodontic instrumentaccording to the present invention. Accordingly, the endodonticinstrument has one or more spiral flutes or grooves. The endodonticinstrument 100 includes a portion for securing the instrument to ahandpiece, and an elongate shaft having cutting edges for shaping thetooth. A portion of the shaft comprises a working length having helicalflutes which form the cutting edges of the endodontic instrument 100. Inuse, the working length of the instrument 100 is inserted into a rootcanal of a tooth through an upper interior portion of the tooth whichhas been initially opened using another instrument, such as a drill (notshown). The instrument 10 of the present invention is adapted for usewith power operated equipment. The instrument 100 may be rotated in thedirection of arrows A and/or reciprocated in the direction of arrow B toclean out and enlarge the root canal. Referring to FIG. 2 b, across-sectional view of a portion of the working length of theinstrument 10 is shown, wherein the helical configuration has beeneliminated for clarity. In the exemplary embodiment shown, theinstrument 10 has two cutting edges defined by two flutes 22 and twoperipheral flute surfaces that extend from the cutting edges to trailingedges, in directions opposite the cutting direction

The endodontic instrument may be an instrument having a diameter at thetip in the range of from 0.20 to 0.35 mm and a taper over the first 3 mmfrom the tip in the range of taper of from 7 to 9% and a diameter D16 inthe range of from 1.00 to 1.10 mm; or an endodontic instrument having adiameter at the tip in the range of from 0.35 to 0.55 mm and a taperover the first 3 mm from the tip in the range of taper of from 5 to 7%and a diameter D16 in the range of from 1.05 to 1.15 mm; or anendodontic instrument having a diameter at the tip in the range of from0.45 to 0.65 mm and a taper over the first 3 mm from the tip in therange of taper of from 4 to 6% and a diameter D16 in the range of from1.12 to 1.22 mm.

In a further embodiment, the system of the present invention may becombined with additional dental devices, such as an apex locator, anendodontic instrument identification system, a vitality tester, aworking length measurement system, a gutta-percha cutter, gutta-perchacondenser, or a photo-polymerization lamp.

According to a preferred embodiment, the system according to theinvention for single file reciprocation without prior use of hand filesincludes three instruments, (R25, R40 and R50), and a motor.

The R25 preferably has a diameter of 0.25 mm at the tip and an 8% (0.08mm/mm) taper over the first 3 mm from the tip. The diameter at D16 is1.05 mm.

The R40 has a diameter of 0.40 mm at the tip and a 6% (0.06 mm/mm) taperover the first 3 mm from the tip. The diameter at D16 is 1.10 mm.

The R50 has a diameter of 0.50 mm at the tip and a 5% (0.05 mm/mm) taperover the first 3 mm from the tip. The diameter at D16 is 1.17 mm.

Only one instrument is used for the canal preparation depending on theinitial size of the canal. Preferably, the instruments are made from anM-Wire nickel-titanium that offers greater flexibility and resistance tocyclic fatigue than traditional nickel-titanium. Preferably, theinstruments have an S-shaped cross-section and a regressive taper.

Preferably, the motor is battery operated. The battery may berechargeable and the motor can be used while the battery is charging.The instruments are preferably used at about 5 to 30, or typically atabout 10 cycles of reciprocation per second. 10 cycles represent theequivalent of approximately 300 rpm. The motor is preferably programmedwith the angles of reciprocation and speed for the three instruments.

When the instrument rotates in the cutting direction it will advance inthe canal and engage dentine to cut it. When it rotates in the oppositedirection (smaller rotation) the instrument will be immediatelydisengaged. The end result is an advancement of the instrument in thecanal. Consequently, only very light apical pressure on the instrumentis required, as its advancement is almost automatic. The angles arespecific to the endodontic instruments and are determined using thetorsional properties of the instruments namely the elastic angle Ψ ofthe endodontic instrument at which plastic deformation occurs in thedirection of α.

The method for operating the system for the endodontic treatment of aroot canal according to the present invention, comprises reciprocatingthe endodontic instrument by continuously sequentially rotating theendodontic instrument in a first direction followed by reversing thedirection of rotation so that 0.5×Ψ≦α<Ψ and 3≦α/β≦20. According to apreferred embodiment, the method may further comprise

-   -   (i) rotating the endodontic instrument in a first rotational        direction to remove material when a control parameter is below a        first threshold value,    -   (ii) reciprocating the endodontic instrument when the control        parameter is greater than or equal to the first threshold value,        and    -   (iii) rotating the endodontic instrument only in the rotational        direction opposite to the first rotational direction in order to        free the instrument, when the control parameter is greater than        or equal to a second threshold value that is greater than the        first threshold value.

According to a preferred embodiment, the control parameter is the torqueapplied to the endodontic instrument.

The method for preparing a root canal with a single file will now beillustrated by the following example. Accordingly, only one endodonticinstrument is usually used in reciprocation to complete the canalpreparation and there is no need for hand filing. The access cavityrequirements, the straight-line access to the canals and the irrigationprotocol are the same as for standard preparation techniques. It is notnecessary to widen the root canal orifice with a Gates Glidden drill oran orifice opener.

Selection of the appropriate endodontic instrument:

Selection of the appropriate endodontic instrument is based on anadequate preoperative radiograph. If the canal is partially orcompletely invisible on the radiograph, the canal is considered narrowand, for example, the R25 is selected. In the other cases, where theradiograph shows the canal clearly from the access cavity to the apex,the canal is considered medium or wide. A size 30 hand instrument may beinserted passively (with a gentle watch winding movement but withoutfiling action) to the working length. If it reaches the working length,the canal is considered large and the R50 may be selected for the canalpreparation. If the size 30 hand file does not passively reach workinglength, a size 20 hand file is inserted passively to the working length.If it reaches working length, the canal is considered medium and the R40may then be selected for the canal preparation. If the size 20 handinstrument does not reach the working length passively, the R25 may beselected.

Preparation step by step (without creating a glide path):

In reciprocation, clockwise and counter clockwise angles determine theamplitude of reciprocation, the right and left rotations. These anglesare lower than the angles at which the endodontic instrument wouldusually fracture (if bound). When a reciprocating file binds in thecanal, it will not rotate past its specific angle of fracture.Therefore, the creation of a glide path to minimize binding is notrequired for the endodontic instruments. The cutting efficiency of theendodontic instruments and the centering ability associated withreciprocation allow the instruments to enlarge uninstrumented and narrowcanals in a safe manner.

Before commencing preparation, the length of the root canal is estimatedwith the help of an adequately exposed and angulated pre-operativeradiograph. A silicone stopper may be set on the instrument at ⅔ of thatlength. The endodontic instrument is introduced in the canal with a slowin-and-out pecking motion without pulling the instrument completely outof the canal. The amplitude of the in- and out-movements shouldpreferably not exceed 3-4 mm. Only very light pressure should preferablybe applied. The instrument will advance easily in the canal in an apicaldirection. After three in- and out-movements, or when more pressure isneeded to make the instrument advance further in the canal, or whenresistance is encountered, the instrument may be pulled out of the canalto clean the flutes. A #10 file may be used to check patency to ⅔ of theestimated working length. The canal may preferably be copiouslyirrigated.

The endodontic instrument is preferably used until it has reached ⅔ ofthe estimated working length as indicated by the stopper on theinstrument. The instrument may then be removed from the canal, the canalmay preferably be irrigated and a #10 file may be used to determine thelength. The endodontic instrument may then be re-used in the same manneruntil the working length has been reached. As soon as the working lengthhas been reached, the endodontic instrument is withdrawn from the canal.The endodontic instrument can also be used in a brushing motion againstthe lateral walls of wide canals. The endodontic instrument will be usedto working length to complete the preparation.

1. A system for the endodontic treatment of a root canal, comprising (i)an endodontic instrument; (ii) an endodontic handpiece having a drivemotor for rotating the endodontic instrument releasably attached to thehandpiece; (iii) a control unit for controlling the rotation of theendodontic instrument according to one or more predetermined rotationalsequences; the rotational sequences comprising reciprocating theendodontic instrument by continuously sequentially rotating theendodontic instrument in a first direction followed by reversing thedirection of rotation so that0.5×Ψ≦α<Ψ and 3≦α/β≦20, wherein α represents a rotational angle in adirection in which the rotating endodontic instrument removes debrisfrom the root canal, β represents a rotational angle in the oppositedirection, and Ψ represents the elastic angle of the endodonticinstrument at which plastic deformation occurs in the direction of α. 2.The system for the endodontic treatment of a root canal according toclaim 1, wherein 0.7×Ψ≦α<0.9×Ψ, and α and Ψ are as defined in claim 1.3. The system for the endodontic treatment of a root canal according toclaim 1 or 2, wherein 4≦α/β≦10, and α and β are as defined in claim 1.4. The system for the endodontic treatment of a root canal according toany one of the preceding claims, wherein the control unit furthercontrols one or more parameters of the rotational sequence, saidparameters being selected from the frequency of reciprocation (F_(r)),the number of reciprocation cycles (N_(r)) and the torque (T_(r))exerted on the file.
 5. The system for the endodontic treatment of aroot canal according to any one of the preceding claims, wherein thecontrol unit controls the frequency of reciprocation (F_(r)) in a rangeof from 5 to 30 Hz.
 6. The system for the endodontic treatment of a rootcanal according to any one of the preceding claims, wherein α, β, F_(r),N_(r), and/or T_(r) are predetermined based on Ψ.
 7. The system for theendodontic treatment of a root canal according to any one of thepreceding claims, wherein the endodontic instrument has an elastic angle(Ψ) in the range of from 120 to 420°.
 8. The system for the endodontictreatment of a root canal according to any one of the preceding claims,wherein the endodontic instrument comprises a NiTi alloy.
 9. The systemfor the endodontic treatment of a root canal according to any one of thepreceding claims, wherein the endodontic instrument has a non-cuttingtip.
 10. The system for the endodontic treatment of a root canalaccording to any one of the preceding claims, wherein the endodonticinstrument has one or more spiral grooves.
 11. The system for theendodontic treatment of a root canal according to any one of thepreceding claims, wherein the endodontic instrument has a diameter atthe tip in the range of from 0.20 to 0.35 mm and a taper over the first3 mm from the tip in the range of taper of from 7 to 9% and a diameterD16 in the range of from 1.00 to 1.10 mm; or wherein the endodonticinstrument has a diameter at the tip in the range of from 0.35 to 0.55mm and a taper over the first 3 mm from the tip in the range of taper offrom 5 to 7% and a diameter D16 in the range of from 1.05 to 1.15 mm; orwherein the endodontic instrument has a diameter at the tip in the rangeof from 0.45 to 0.65 mm and a taper over the first 3 mm from the tip inthe range of taper of from 4 to 6% and a diameter D16 in the range offrom 1.12 to 1.22 mm.
 12. The system for the endodontic treatment of aroot canal according to any one of the preceding claims, wherein thedrive motor is battery operated.
 13. A method for operating the systemfor the endodontic treatment of a root canal, the method comprisingreciprocating an endodontic instrument by continuously sequentiallyrotating the endodontic instrument in a first direction followed byreversing the direction of rotation so that0.5×Ψ≦α<Ψ and 3≦α/β≦20, wherein α represents a rotational angle in adirection in which the rotating endodontic instrument removes debrisfrom the root canal, β represents a rotational angle in the oppositedirection, and Ψ represents the elastic angle of the endodonticinstrument at which plastic deformation occurs in the direction of α.14. The method for operating the system for the endodontic treatment ofa root canal according to claim 12, wherein method further comprises(iv) rotating the endodontic instrument in a first rotational directionto remove material when a control parameter is below a first thresholdvalue, (v) reciprocating the endodontic instrument when the controlparameter is greater than or equal to the first threshold value, and(vi) rotating the endodontic instrument only in the rotational directionopposite to the first rotational direction in order to free theinstrument, when the control parameter is greater than or equal to asecond threshold value that is greater than the first threshold value.15. The method for operating the system for the endodontic treatment ofa root canal according to claim 12 or 13, wherein the control parameteris the torque applied to the endodontic instrument.